The degree of integration of integrated circuits has recently become much higher, and the processing of superfine patterns having a line width of a half micron or below is required in the production of semiconductor substrate for VSLI, etc. In order to meet such a requirement, a wavelength of light source used in an exposure apparatus for photolithography becomes shorter, and nowadays the use of an excimer laser beam (e.g., XeCl, KrF or ArF) in a short wavelength region of a far ultraviolet ray is investigated.
As a resist for use in the pattern formation by the photolithography in such a wavelength region, a chemically amplified resist is known.
In resist compositions for ArF light source, resins having an alicyclic hydrocarbon moiety introduced for the purpose of providing dry etching resistance have been proposed.
In Patent Document 1 (JP-A-9-73173 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”)), there is described a resist material using an acid-susceptive compound containing an alkali-soluble group protected by a structure including an alicyclic group and a structural unit capable of rendering the resin alkali-soluble upon releasing the alkali-soluble group by an acid.
In Patent Document 2 (JP-A-2000-214588) and Patent Document 3 (JP-A-2000-321771), resist compositions comprising a copolymer containing a methacrylic acid or acrylic acid repeating unit and an acid-decomposable repeating unit are described.
In Patent Document 4 (JP-A-2001-188351) and Patent Document 5 (JP-A-2000-26446), resist compositions comprising a copolymer containing a repeating unit having an alicyclic lactone structure are described.
In Patent Document 6 (JP-A-7-252324) and Patent Document 7 (JP-A-11-109632), resist compositions comprising a copolymer containing a repeating unit having an alicyclic group substituted with a hydroxy group are described.
In Patent Document 8 (JP-A-2001-109154) and Patent Document 9 (JP-A-2002-296783), a combination of an acid-decomposable repeating unit, a repeating unit having an alicyclic lactone structure and a repeating unit having an alicyclic group substituted with a hydroxy group is described.
Resins used in photoresist for far ultraviolet ray as described above ordinarily contain an acid-decomposable group and an aliphatic cyclic hydrocarbon group at the same time in the molecules thereof.
With respect to application of such conventional resins having alicyclic hydrocarbon moiety introduced to a resist composition, further improvements in various performances have been desired. Among them, further enlargement of process window of resist for contact hole has been requested.
Further, for the exposure of resist used in photolithography, a reduction production exposure method with a radiation (for example, g-line, i-line or KrF excimer laser beam) has been utilized. In general, resolution (R) of a lens is represented by the following formula according to the Rayleigh's equation:R=k[λ/N.A.]
In the formula, λ represents a wavelength of exposure light and N.A. represents a numerical aperture of the lens. Designating an open angle of incident light to a wafer as θ, N.A.=sin θ. k indicates a value fluctuating according to a resist and is frequently used as a characteristic parameter exhibiting performances of the resist. According to knowledge on a resist for i-line, k becomes small only as approximately 0.5, even when the resist is improved. As is apparent from the formula, in order to increase the resolution, R must be a small value. For this purpose, it is desired to increase the value of N.A., to decrease the value of λ or to decrease the value of k. At the present circumstances, however, the value of N.A. increases to reach almost 0.8 and on the other hand, the value of k reaches the limit of 0.5. In view of making the wavelength for exposure shorter, investigations have been made from 248 nm of KrF excimer laser beam to 193 nm of ArF excimer laser beam. However, even when the ArF excimer laser beam is used, the pattern formation of 100 nm or less becomes theoretically difficult.
Thus, a resist material capable of forming a finer pattern and a method of forming a pattern using a current exposure apparatus have been requested. In response to such requests, a technique including a method of controlling a contact hole size of a semiconductor device wherein a wafer is heated while irradiating with an ultraviolet ray (UV) in vacuo (flow bake) to change a resist shape (flow), thereby reducing a size of resist pattern as described in Patent Document 10 (JP-A-6-37071) appears promising. However, development of resist material suitable for the method is insufficient. Further, since the process of flow bake of a wafer while irradiating with an ultraviolet ray in vacuo is troublesome, a resist material capable obtaining the same effect only by flow bake in the atmosphere has been desired. However, when the flow bake process is applied to hitherto known resist materials, there are problems in that the control of hole size is difficult because of high flow speed and in that the resist materials do not sufficiently flow at a practical flow temperature (180° C. or below).
Recently, it has been further found that pits are frequently formed in a film at the flow bake step. There is fear that the formation of pits causes adverse effects (for example, deterioration of pattern transferability after etching or deterioration etching resistance) on a subsequent etching step. Therefore, it has been desired to prevent the formation of pits.
Patent Document 1 (JP-A-9-73173)
Patent Document 2 (JP-A-2000-214588)
Patent Document 3 (JP-A-2000-321771)
Patent Document 4 (JP-A-2001-188351)
Patent Document 5 (JP-A-2000-26446)
Patent Document 6 (JP-A-7-252324)
Patent Document 7 (JP-A-11-109632)
Patent Document 8 (JP-A-2001-109154)
Patent Document 9 (JP-A-2002-296783)
Patent Document 10 (JP-A-6-37071)